The present invention relates to the cardiac valve prostheses, also called "cardiac mechanical prostheses", since they are effective to provide the operation of the cardiac valves, while being of different anatomic construction.
As it is known, the surgery of the cardiac valve diseases only rarely adopts conservative methods, since, very frequently, the cardiac valve lesions are so serious that they require a complete extirpation of the sick cardiac valve apparatus, to be replaced with artificial valves.
The main and most important features that an artificial cardiac valve must have to approach as far as possible an ideal cardiac valve are: (a) a nearly unlimited duration (b) a perfect acceptance by the host and/or hostess, in particular by the endocardic tissues whereof, (c) a hemodynamic function, that is a circulation function, as far as possible equal to that of a normal cardiac valve, with respect to the facility of installation.
In this field, intensive researches have been made for finding such a cardiac valve effective to satisfactorily meet the thereinabove stated requirements.
One of these valves is the Starr valve, which consists of a Teflon ring supporting a metal cage in the inside whereof a ball is located.
This ring acts as a valve seat, the ball as a shutter and the cage as a guide for the ball stroke. Thus, the Starr valve can be considered as a conventional ball valve as those used in the fluid dynamic field.
Another artificial cardiac valve which has given good results, consists of a special plastic material ring, well compatible with the endocardiac tissue, and acting as a valve seat provided on the outside thereof with a peripheral groove effective to receive or house a ring member also made of a special plastic material cloth and provided for acting as an anchoring member for tying yarns as applied to the host tissue. The valve seat forming ring is provided with two small and thin lugs, projected to the inside and effective to engage with two arms rigid with a plate member effective to act as a valve shutter and to provide a loose pivoting coupling.
In this case, the cardiac valve can be considered as a conventional hinge valve, as used in the industry, and it eliminates the drawback related to the fixing of the cage member of the Starr valve.
However, these artificial valves are not devoid of drawbacks. More specifically, they compel the man/woman thereto the valve is fitted to submit to a daily anticoagulating treatment to reduce to a minimum the possibility of fibrinous deposits or coagula on the artificial valve structures, particularly those which are located in the blood stream and which are engaged thereby. For example, in the Starr valve, these structures consist of the metal cage and the ball and, in the hinge type of valve, they consist of the lugs and pivoting arms of the plate member.
The fibrinous deposits or coagula, in time, either because of mechanical effects of the ball or pivoting lugs or due to other reasons, can cause the detachement of valve portions which, as conveyed by the blood stream, can be brought towards the peripheric arteries, thereby causing embolisms to occur, which are sometimes very serious, especially if the embolus locates in the brain.
The hinged plate type of valve, though it has the feature of determining smaller fibrinous deposits or coagula, due to the smaller surface exposed to the blood stream, presents however the drawback that, in time, since the opening of the plate member is restrained by the lugs and the arms, it is not effectively complete and becomes smaller and smaller, due to the aforesaid deposits, thereby a narrowing of the blood flow rate through the valve occurs, with a consequent stanching of the blood in the cardiac cavities and possible cardiac decompensation.